Paraxanthin

Paraxanthine is a xanthine alkaloid, specifically 1,7-dimethylxanthine, and is one of the principal metabolites of caffeine. It is produced in humans through hepatic N-demethylation of caffeine, a reaction mediated mainly by the enzyme cytochrome P450 1A2, alongside theobromine and theophylline as other major metabolites.

Paraxanthine is a major metabolite, frequently the most abundant one in human plasma after caffeine administration. Its formation reflects individual variation in caffeine metabolism and contributes to the overall pharmacokinetic profile of caffeine-derived activity.

Pharmacologically, paraxanthine, like caffeine, acts as a non-selective antagonist of adenosine receptors. This antagonism is thought to contribute to stimulant effects, such as increased wakefulness and alertness, though paraxanthine’s potency is generally somewhat lower than that of caffeine. The compound shares several physiological effects with caffeine but with differences in potency and onset of action.

Pharmacokinetically, paraxanthine is rapidly formed after caffeine intake and subsequently metabolized and excreted in urine. The elimination half-life varies widely among individuals and can be influenced by genetics, age, liver function, smoking, and concurrent medications.

In research and clinical contexts, paraxanthine is used as a biomarker of caffeine metabolism and is measured in studies of caffeine intake and disposition. It is related to other methylxanthines such as caffeine, theobromine, and theophylline.